Why Do Some OLEDs Have Motion Blur?

First published March 13th, 2013

Written by Mark Rejhon (aka Chief Blur Buster)

OLED has been regarded as a Holy Grail for eliminating motion blur. Unfortunately, not always: The portable Playstation Vita and Samsung Galaxy S3 have lots of motion blur during fast scrolling animations. They are not low-persistence OLEDs.

Why?

The answer lies in persistence (sample-and-hold). OLED is great in many ways, however, many of them are hampered by the sample-and-hold effect. Even instant pixel response (0 ms) can have lots of motion blur due to sample-and-hold. Some OLEDs use strobing for lower persistence, to eliminate motion blur, but not all of them do.

Your eyes are always moving when you track moving objects on a screen. Sample-and-hold means frames are statically displayed until the next refresh. Your eyes are in a different position at the beginning of a refresh than at the end of a refresh; this causes the frame to be blurred across your retinas:

The flicker of impulse-driven displays (CRT) shortens the frame samples, and eliminates eye-tracking based motion blur. This is why CRT displays have less motion blur than LCD’s, even though LCD pixel response times (1ms-2ms) are recently finally matching phosphor decay times of a CRT (with medium-persistence phosphor). Sample-and-hold displays continuously display frames for the whole refresh. Persistence (sample-and-hold) is a different measurement from pixel transitions (GtG). As a result, a 60Hz refresh (even on “2ms GtG” LCDs) is displayed for a whole 1/60th of a second (16.7ms persistence).

Motion blur occurs on the Playstation Vita OLED even though it has virtually instantaneous pixel response time. This is because it does not shorten the amount of time a frame is actually visible for, a frame is continuously displayed until the next frame. The sample-and-hold nature of the display enforces eye-tracking-based motion blur that is above-and-beyond natural human limitations.

Solution to Motion Blur

The only way to reduce motion blur caused by sample-and-hold, is to shorten the amount of time a frame is displayed for. This is accomplished by using extra refreshes (higher Hz) or via black periods between refreshes (flicker).

Some experimental OLED televisions now shorten frame sample lengths by strobing the pixels, and/or motion interpolation (extra refreshes). Motion interpolation can interfere with video games due to input lag. Fortunately, impulse-driving (flicker) is video game friendly.

One big problem to overcome first, is that impulse-driving require a lot of brightness to compensate for extra black period between refreshes. OLED has historically had brightness problems, however, researchers are continually improving this.

Tests on Sony Professional OLED

Recently, several researchers (Hiroyuki Ito, Masaki Ogawa and Shoji Sunaga) have published OLED responsiveness findings about the Sony Trimaster PVM-2541, a Sony OLED display targeted at the professional markets.

This active-matrix OLED is impulse-driven at 7.5 milliseconds per pixel via a rolling scan, and has roughly equivalent motion blur as 120Hz non-LightBoost computer monitors, and LightBoost still outperforms OLED with as little as 1.4 milliseconds of measured motion blur (see 60Hz vs 120Hz vs LightBoost). As of 2013, most strobe-backlight gaming monitors today (see List of 120Hz/144Hz Monitors) has lower persistence than OLED.

“Flicker Fusion”
by Stephen Macknik, Barrow Neurological Institute (Scholarpedia)Background information that relates to how flicker becomes a continuous image (applies to CRT and to scanning backlights).

“Temporal Resolution”
by Michael Kalloniatis and Charles Luu, Webvision (University of Utah)Background information that relates to human vision behavior and how multiple flicker events, over a short interval, blends together.

I have new receiver Dreambox 800 HD SE w/ Wi-Fi. The mini-OLED color of this receiver is PMOLED and gets 100% flicker (flicker is never any “soft” as CRT and VFD screens),
But unfortunately any PMOLED has currently small screen with up to 5″ and up to 262k-color. But in future may have bigger screen PMOLED.

NOTE: We remember I don’t login in your forum because I don’t receive any message by email yet after send password forgotten.

Thanks for the great explanations.
However one point remains unclear or at least I could not get it.
Although the blackframe insertion solves the problem of motion blur within one single frame still the brightness of the individual pixels has to be controlled by some dimming.

How is this usually done for oled displays using blackframe insertion?
Is there still a pwm, much faster than the time where the image is shown or is there any other technique?